Device Monitor - a tool for automatic network device monitoring and detection

[mooh]

Not every plugin is for everyone — install what fits your needs. 🙂

I didn't mean to belittle your effort. In fact, I appreciate every effort to improve OPNsense.

I just not sure what the size of the target audience for all this host discovery stuff is, yours and the new component of OPNsense. If I want to know what's going on on my network, I ask it directly via SNMP or an all-in-one solution like Unifi or Omada. Only small, unmanaged networks don't already provide that functionality. How many are there using OPNsense?

[pc44]

I have an older version of Device Monitor installed and working.  It is great !!!

I am happy with it, but is there a way to update to this new version, or do I need to fully uninstall/reinstall?

Thank you.

[SteffenDE]

Hi Steffen,
The hostname field works as follows: the plugin pulls the hostname from Services → ISC DHCPv4 / DHCPv6 → DHCP Static Mappings — specifically the Hostname field for each entry. If a device doesn't have a static mapping with a hostname defined there, the field will simply remain empty, as the plugin has no other automatic source for this information.
You can also fill in the hostname manually directly in the plugin, but note that this is stored only in the plugin's own database — it does not propagate back to OPNsense DHCP or any other system.
So the short answer: populate the Hostname field in your DHCP static mappings and it will appear automatically.

I have hostnames defined at Dnsmasq because I think ISC is deprecated. So it would be nice to support Dnsmasq too.

[pc44]

I have an older version of Device Monitor installed and working.  It is great !!!

I am happy with it, but is there a way to update to this new version, or do I need to fully uninstall/reinstall?

Thank you.

Figured it out.  Deleted the existing /tmp/opnsense-devicemonitor folder.  Then downloaded, unzipped, and copied over the new files.  Then just re-ran sh install.sh.

Now up-to-date. ☑️

[hacesoft]

I have an older version of Device Monitor installed and working.  It is great !!!

I am happy with it, but is there a way to update to this new version, or do I need to fully uninstall/reinstall?

Thank you.

Figured it out.  Deleted the existing /tmp/opnsense-devicemonitor folder.  Then downloaded, unzipped, and copied over the new files.  Then just re-ran sh install.sh.

Now up-to-date. ☑️

Good day, exactly as you asked. If you use sh install.sh, everything except the database will be deleted before installation. After installation, the plugin will be started again. If you use sh uninstall.sh, everything will be removed.

[hacesoft]

Hi Steffen,
The hostname field works as follows: the plugin pulls the hostname from Services → ISC DHCPv4 / DHCPv6 → DHCP Static Mappings — specifically the Hostname field for each entry. If a device doesn't have a static mapping with a hostname defined there, the field will simply remain empty, as the plugin has no other automatic source for this information.
You can also fill in the hostname manually directly in the plugin, but note that this is stored only in the plugin's own database — it does not propagate back to OPNsense DHCP or any other system.
So the short answer: populate the Hostname field in your DHCP static mappings and it will appear automatically.

I have hostnames defined at Dnsmasq because I think ISC is deprecated. So it would be nice to support Dnsmasq too.

Good day, I just converted my home network from ISC to DNSmasq and it will take a while before I get to it and modify the plugin. but don't worry, it will happen :).

[hacesoft]

Not every plugin is for everyone — install what fits your needs. 🙂

I didn't mean to belittle your effort. In fact, I appreciate every effort to improve OPNsense.

I just not sure what the size of the target audience for all this host discovery stuff is, yours and the new component of OPNsense. If I want to know what's going on on my network, I ask it directly via SNMP or an all-in-one solution like Unifi or Omada. Only small, unmanaged networks don't already provide that functionality. How many are there using OPNsense?

Hello, I recently switched from pfSense to OpnSense and this option was standard in the system and I use it to check if an uninvited guest is connecting. Or when I connect a device, I find out its IP address. I don't have unifi, or rather I only use AP AC RL and I have a classic L2, L3 switch. So OpnSense will provide me with the necessary information :). I originally wrote the plugin just for myself, but I decided to share it with others... I would like the plugin to be offered as a standard package, but that's too much for me for now :).

[hacesoft]

Good day, I have released version 2.1. which supports Dnsmasq DNS & DHCP.
Again I look forward to your reactions :).

The link is:

https://github.com/hacesoft/opnsense-devicemonitor

[lnet.admin]

Good day, I have released version 2.1. which supports Dnsmasq DNS & DHCP.
Again I look forward to your reactions :).

The link is:

https://github.com/hacesoft/opnsense-devicemonitor

Thank you for this, that's better - my Hostnames are now correct.

[apg1959]

Hi,

I'm running OPNsense 26.7.2_2 with Device Monitor v2.1.

I found an issue where multiple historical Hostwatch records for the same MAC address can cause Device Monitor to select an old IP/interface record instead of the current one.

Example

My Windows PC has:

MAC: 7c:83:34:b2:34:7c
Current IP: 192.168.20.111
Interface: igc1 / LAN

Device Monitor initially showed this device incorrectly as:

IP: 192.168.20.146
Interface: IGC1
Offline

I checked the Hostwatch database directly:

sqlite3 /var/db/hostwatch/hosts.db \
"SELECT interface_name, ip_address, ether_address, first_seen, last_seen, organization_name
FROM v_hosts
WHERE ether_address='7c:83:34:b2:34:7c';"

Hostwatch contained three records for the same MAC:

igc1  192.168.20.146  2026-08-15 03:04:46
igc0  192.168.20.146  2026-08-15 11:10:03
igc1  192.168.20.111  2026-08-19 06:06:49

The last record is the current/correct one.

I also confirmed Hostwatch itself was updating correctly. For example, its most recent records included:

7c:83:34:b2:34:7c  192.168.20.111  igc1  2026-08-19 06:08:51

So Hostwatch was not the problem.

Cause

I traced this to:

/usr/local/opnsense/scripts/OPNsense/DeviceMonitor/scan_network.py

The Hostwatch query currently retrieves all matching records:

SELECT
    interface_name,
    ip_address,
    ether_address,
    first_seen,
    last_seen,
    organization_name
FROM v_hosts
WHERE protocol = 'inet'
  AND ether_address NOT IN ('ff:ff:ff:ff:ff:ff', '00:00:00:00:00:00')
  AND ip_address NOT LIKE '169.254.%'
ORDER BY last_seen DESC

There is no deduplication by ether_address.

Device Monitor's own database uses the MAC address as the key:

mac TEXT PRIMARY KEY

Therefore, when multiple Hostwatch records exist for the same MAC, they are processed sequentially and can overwrite one another. In my case, the historical .146 record ended up being stored instead of the current .111 record.

This also affected the Online/Offline status because Device Monitor was evaluating the stale record's last_seen.

Test fix

I tested a local modification to the SQL query which selects only the newest last_seen record for each MAC address, with the Hostwatch id used as a tie-breaker.

After applying the change and running a full scan, Device Monitor immediately changed the affected PC to:

MAC:      7c:83:34:b2:34:7c
IP:        192.168.20.111
Interface: IGC1
Status:    ONLINE

The Device Monitor database then showed:

7c:83:34:b2:34:7c
192.168.20.111
IGC1
2026-08-19 06:18:58
is_active = 1

I subsequently restarted Device Monitor and confirmed the service restarted normally and the Devices page continues to show the correct IP/interface/status.

Suggested fix

I believe the Hostwatch query should deduplicate records by ether_address and select the record with the newest last_seen before passing the results to the Device Monitor database.

This would prevent historical Hostwatch records from overwriting the current record for the same MAC.

The email notification functionality otherwise works correctly for me. I have successfully tested detection of a new MAC address and received the Device Monitor email notification through Postfix.

Thanks — I've attached modified SQL/query if useful.